1. Field of the Invention
The present invention relates in general to tilt steering devices for wheeled motor vehicles, and more particularly to the tilt steering devices of an electrically powered type, which tilt a steering shaft with electric power. The steering devices of this type will be referred to an electrically powered tilt steering device in the following.
2. Description of the Related Art
Hitherto, in the field of wheeled motor vehicles, various types of electrically powered tilt steering devices have been proposed and put into practical use. In such tilt steering devices, an electric motor is used for driving a tilting mechanism incorporated with a steering device.
In order to clarify the task of the present invention, one of hitherto proposed electrically powered tilt steering devices will be briefly described in the following, which is disclosed in Japanese Laid-open Patent Application (Tokkai) 2007-83992.
In the electrically powered tilt steering device of the publication, there is employed an electrically powered tilting mechanism that changes the height (or angular position) of a steering wheel on a steering shaft (or steering column) with electric power. That is, tilting of the steering wheel is carried out by the electrically powered tilting mechanism.
The known electrically powered tilt mechanism comprises a jacket unit that rotatably receives therein a steering shaft that has a steering wheel connected to a top thereof. The jacket unit is pivotally supported by a vehicle body through a pivot mechanism. A swing arm is pivotally connected to the vehicle body through another pivot mechanism. A first free part of the swing arm is pivotally connected to the jacket unit. A screw rod member is rotatably held by the jacket unit through first and second holding structures, and a nut member is operatively engaged with the screw rod member, so that rotation of the screw rod member about an axis thereof induces an axial movement of the nut member on and along the screw rod member. The nut member is pivotally connected to a second free part of the swing arm. One end of the screw rod member is driven by an electric motor through a speed reduction unit.
For rotatably mounting the screw rod member on the jacket unit, the first holding structure that is to be placed near the motor driven end of the screw rod member is assembled, then the second holding structure that is to be placed away from the motor driven end of the first threaded rod member is assembled, then the screw rod member is put into the assembled first and second holding structures, and then, an externally threaded retainer is screwed into a threaded bore of the second holding structure to retain a bearing in the second holding structure. With these steps, the screw rod member is rotatably held by the first and second holding structures.